im a lil confused i jsut read a post in which some turbo car owner was talking about they got less hp at 6000 feet than at sea level. Messing with planes a lot of my life i swore turbochargers made up for the lack of air density.. i thought you just spool the turbo more to get the same hp out for a turbo car.. you dont build more boost just just spool the turbo faster. i went to new mexico where the altitudes were 6500 to 8500 and i just made the huge turbo work harder to produce the same about of boost. make sense? am i on the wrong page and on the way to blowin up my shiznit? i dont think so

 

In theory, yes a turbo car should maintain its output regardless of altitude, at least within the relatively narrow range of altitude cars operate in. However, I believe in practice this is not always so, and depends on whether the car determines max boost in terms of an absolute (eg, psi) or relative (bar) measure. I don't recall the specifics of it, but I believe in the case where boost is calculated as an absolute measure the system will maintain full boost and therefore hp, as long as the turbo can be run up to the higher speeds necessary. Whereas if boost is relative (eg, boost is limited to 1.0 bar or 1.5 bar, etc), the engine will still loose horsepower with altitude, since it is only allowing a certain amount of boost relative to ambient air pressure - the car still won't loose as much HP as an NA engine, but will loose power nonetheless.

 

While a turbo will theoretically just spin faster to make up the air density difference, you have to remember that it is spinning faster to do this and making more heat. This is a loss of efficiency. A turbo engine just loses less power as altitude rises. You will eventually come to a point in altitude that the turbo can't supply enough air anymore to maintain the same pressure.

 

GXL biscuit, look over the owners manual of the next turbo/supercharged airplane you fly. You'll see that its full HP rating is guaranteed up to a certain altitude. Turbos typically hit an rpm limit (shaft speed limited) that limits their ability to produce the same amount of pressure/airflow at higher altitudes.

My non-RX7 turbo vehicle's turbo is unable to produce sea-level power above 5,000 feet altitude. I live at 7,000 altitude and can notice the difference when I drive to much lower elevations.

 

stab stab twist break..... never flown a turbo plane:-P my turbo is bigger than my engine will ever need.... bnr stage 3 on stock ports....